1. Field of the Invention
The present invention relates to a heat exchanger suitable for use in a vehicle air conditioning system and, more particularly, to a structure for connecting heat transfer tubes to heat exchanger reservoirs.
2. Description of the Related Art
FIG. 8 depicts a conventional heat exchanger for use in a vehicle air conditioning system. A heat exchanger 61 comprises an upper reservoir 62 and a lower reservoir 63. A plurality of heat transfer tubes 64 are fluidly connected between upper and lower reservoirs 62 and 63. A heat transfer medium, for example refrigerant, flows from an inlet pipe 65 to an outlet pipe 66. Generally, the heat transfer medium flows through the interior of upper reservoir 62, down heat transfer tubes 64, through the interior of lower reservoir 63, up heat transfer tubes 64, and through the interior of upper reservoir 62, thereafter exiting from outlet pipe 66. The heat transfer medium flowing through tubes 64 exchanges heat with outside air passing between tubes 64.
In a conventional heat exchanger, heat transfer tubes 64 are typically connected to upper and lower reservoirs 62 and 63, for example, in such a manner as shown in FIG. 9. In FIG. 9, an end portion 67 of heat transfer tube 64 is inserted into an interior of upper reservoir 62 through hole 68 formed in the reservoir wall. The periphery of end portion 67 is connected to the surface of hole 68. This connection is typically achieved by brazing. End portion 67 of heat transfer tube 64 projects into the interior of reservoir 62 to a projection length B. Heat transfer tubes 64 are typically connected to lower reservoir 63 in the same manner.
Because end portion 67 of each heat transfer tube 64 projects into the interior of reservoir 62, a dimension A of reservoir 62 in the longitudinal direction of tubes 64 must be designed taking into account projection length B. As projection length B increases, dimension A also increases, thereby increasing the size of upper reservoir 62. Thus, the total size of heat exchanger 61 also increases. As the size of reservoirs 62 and 63 increases, the proper volume of heat transfer medium to be circulated in heat exchanger 61 also increases. Regardless of the care taken in designing heat exchanger 61, minimization of the size of reservoirs 62 and 63 is limited by the projection of end portions 67.
Another disadvantage of the conventional heat exchanger is that the flow of a heat transfer medium in reservoirs 62 and 63 is obstructed by end portions 67 projecting into reservoirs 62 and 63. This obstruction of flow typically causes a pressure loss in the flow circuit of the heat transfer medium.
Another disadvantage is that the surface area for brazing heat transfer tubes 64 to reservoirs 62 and 63 is typically small. Thus, the strength of the connections therebetween might be insufficient. This presents particular problems, for example, when heat exchanger 61 is disposed in a vehicle engine compartment where it is subjected to extended periods of vibration. In such a situation, it is often difficult to ensure sufficient reliability of the strength of the connections between tubes 61 and reservoirs 62 and 63.